The Use of Boiler Flue Gases for Absorption Lithium Bromide Heat Pumps in the System of Regenerative Heating of Make-up Water

Increasing the efficiency of primary energy sources use in the production of heat and electricity at thermal power plants is an enduring task in the context of reducing the cost of converted energy flows production and improving the environmental characteristics of a power gene-rating unit. To solve this problem, it is proposed to develop a system for regenerative heating of feedwater via the use of low-temperature waste heat flows from a thermal power plant, which is possible with the integration of heat-recovery heat pumps into the thermal scheme of the station. In this paper, we consider the use of the aforementioned lithium bromide absorption heat pumps driven by flue gases extracted from the steam boiler path and the circulating water stream of the condenser is used as a source of low-potential energy. Depending on the efficiency function, when optimizing the operating mode of the power plant in accordance with the requirements of the power system after modernization, it is possible to reduce the electric power of the turbine, increase it or maintain it at the same level. For each of the three variants, a numerical experiment was conducted for the PT-60 turbine unit, which is the most common in the unified Belarusian Energy System. For the option with a decrease in electrical power, the following results were obtained: an increase in electrical, energy and exergetic efficiency, respectively, amounted to 4.3, 2.6 and 1.1 %, while also reducing the temperature of outgoing flue gases due to their deeper cooling to 110 °C. The paper determines the cross-sections of the gas-air duct of the boiler unit for the selection of flue gases with a temperature that ensures the operation of the absorption heat pump at nominal parameters. The flue exhaust gases of the lithium bromide absorption heat pumps are mixed with the flue gas stream directly from the boiler before being discharged into the smokestack.